The task is a complicated one because, in general, Washington museums are well protected and greatly improved their procedures after the Sept. 11, 2001 terrorist attacks. Also, an armed presence and checkpoints seem to go against the museum culture of being safe and open destinations for accessing beauty, education and entertainment.

But in the aftermath of the killing of a security guard at the U.S. Holocaust Memorial Museum on Wednesday, allegedly by white supremacist James Wenneker von Brunn, museum officials were taking another look.

"We are all reviewing what we are doing and asking are we doing enough," said Joe Urschel, the executive director and senior vice president of the Newseum. The facility is a major presence on Pennsylvania Avenue NW, and visitors there go through magnetometers. "Yesterday we had discussions with the head of our security office and increased the presence of security around our perimeter," said Urschel. The museum has unarmed security staff working every day and an armed off-duty police officer at the museum on a regular, but not daily basis, Urschel said. Now one of the questions is: "Should we increase that presence?" he said.

The Smithsonian Institution uses a variety of inspection techniques for visitors, including bag checks, which are mandatory at all its facilities. The major museums on the Mall -- the National Air and Space Museum, the National Museum of Natural History and the National Museum of American History -- use magnetometers. Some of their guards are armed, while all officers at the National Zoo, who are part of a special police force, are armed.

Yesterday, the Smithsonian relocated a few guards to improve surveillance efforts. In fiscal 2009, the Smithsonian received about $60 million for its security needs from Congress; as part of that, it plans to hire more security guards this year and to continue placing concrete barriers near its buildings.

"The guard force is constantly trained to react to certain circumstances, such as swine flu or the inauguration," said Smithsonian spokeswoman Linda St. Thomas.

The Corcoran Gallery of Art and College of Art and Design has had special procedures because of its proximity to the White House, and events on Wednesday tested their effectiveness. Extra guards were detailed to the 17th Street main entrance area.

"We went onto an emergency channel on the radios. All the guards immediately stood up at their posts, both at the entrances and the galleries," said Debbie Jones, the Corcoran's director of security and safety. She informed her staff of the status of the crisis at the Holocaust Museum and proceeded with the emergency measures until one hour after the suspect was taken into custody. Yesterday Jones returned security to its normal formation and held a meeting with the staff of 36. "Everybody thought the plan worked well," she said.

The Smithsonian's Anacostia Community Museum, which focuses on African American history and culture, said it had not received any threats in the wake of Wednesday's shooting, and did not have any plans to increase its security. The Jewish Historical Society of Greater Washington, which operates a museum, said it is maintaining its current safety procedures.

"We didn't change anything, but it gave us an opportunity to review our policies. Two years ago we were the recipients of a homeland security grant. With that, our improvements gave us a better ability to see and screen our visitors before they get in the door," said Laura Cohen Apelbaum, executive director of the society. She said many Jewish organizations take advantage of an informal network to warn about threats anywhere in the country. "In the Jewish community we are sensitized to these troubles," Apelbaum said.

The unique role of museum security guards was a popular topic of conversation yesterday among museum executives. Ford W. Bell, the president of the American Association of Museums, said museums "have always been among the most safe and secure of public institutions, and museum staff work every day to ensure that they remain so. We all salute the courage and professional action of security staff and law enforcement in resolving this situation." The Corcoran's Jones said the museum standard is a "soft security presence, relaxing, non-hassling."

The security force is not just there for the protection of the artifacts or the visitors, said Brent D. Glass, director of the American History Museum. "They are part of our hospitality and way-finding. They wear a lot of hats and people expect them to know details."

One of the questions museums are confronting after Wednesday's shooting, Glass said, involves deployment -- whether there are enough security people at certain crowded areas. "We will be looking at staffing levels," said Glass, who sounded a cautionary note. "We are always reacting. We are always planning for the last incident. It is something that can't be over-emphasized, but we can't always predict what the next challenge will be. The security barriers are anticipating cars, and in this case this guy just walked in."

All of the museums spoke of the loss of Stephen T. Johns, the guard killed at the Holocaust Museum, as a shared tragedy. At the National Gallery of Art, the museum and U.S. flags were lowered to half-staff. The Smithsonian lowered its institutional flags.